A number of techniques exist for forming a corrosion resistant coating on metal parts. One such process is disclosed in my co-pending application filed on even date herewith entitled "Cathodic Electrodeposition Process," the entire disclosure of which is incorporated herein by reference. Therein, a process is disclosed in which a plurality of electrically conductive, small metal parts are placed in a pretreatment barrel. The parts are pretreated by sequentially immersing the barrel in a first series of tanks containing phosphating and rinse solutions. A phosphate coating is formed on the surface of the parts in the barrel to provide increased corrosion resistance. The phosphated parts are then transferred from the pretreatment barrel to a cathodic E-coat barrel in which the parts are coated with a heat-curable organic film by electrodeposition. The coated parts are transferred from the electrodeposition barrel to a conveyor. The conveyor moves the coated parts through a curing oven where the organic coating is cured by infra-red lamps. It has been found that this method is extremely efficient for electro-coating small metal parts which are difficult to process using prior art techniques. The coatings produced using this method are durable and have a minimum number of touch points or gaps in the coating. The method is particularly suited for coating parts with threaded portions and similar fine structures.
As will be appreciated by those skilled in the art, a number of problems are inherent in the equipment used in many prior art electrodeposition lines which make such lines difficult to automate and which interfere the ability to obtain a uniform surface coating on all parts in a bulk treatment operation. In those applications in which it is important to avoid gaps in the surface coating, prior art techniques may require that the parts undergo multiple paint cycles and the like. For example in U.S. Pat. No. 5,104,507, "Anodic-Cathodic Coating for Fasteners" it is disclosed that it is necessary to apply at least two separate electrodeposition operations with an interim curing stage in order to obtain complete coverage. In U.S. Pat. No. 4,165,242, "Treatment of Metal Parts to provide Rust-Inhibiting coatings by Phosphating and Electrophoretically depositing a Siccative Organic Coating," it is disclosed that improved corrosion resistance of small metal parts can be obtained through the application of a final surface layer of a petroleum oil as a top coat. Therein, the parts are first phosphated and electro-coated prior to application of the oil top coat.
Accordingly, it is an object of the present invention to provide automated equipment for the bulk treatment of metal parts in which the surface of the parts is modified in successive stages to provide a superior corrosion resistant coating.
It is also an object to provide a carriage for a treatment barrel that allows vertical movement of the carriage and rotational movement of the barrel without the permanent attachment of an electrical cable to the carriage.
It is also an object of the present invention to provide an apparatus for transferring small metal parts from a first treatment barrel to a second treatment barrel in an electrodeposition line.
It is still a further object of the present invention to provide an overall automated electrodeposition line which utilizes barrel immersion technology to form coatings on small metal parts without the disadvantages of prior art batch processing systems.
It is still a further object of the present invention to provide a substantially fully automated phosphating and electrodeposition coating line in which a phosphate coating and a cathodically applied organic top coat are applied sequentially without cross contamination of the processing equipment.